This chapter reviews steps in the laboratory construction of basic appliances and discusses their indications and their mode of activation. For other appliances, whose fabrication is more complex, the finished appliance is presented.

Expansion Appliances

Quadhelix

This appliance, devised by Ricketts, consists of a palatal arch, shaped like a W, in which four helical loops are incorporated to increase its inherent flexible power.

Laboratory steps

For use in the primary dentition, we prefer to make the quadhelix with 0.032 blue Elgiloy wire; for the mixed and permanent dentitions, we use 0.036 wire. The quadhelix can be either removable or soldered. The construction of a removable quadhelix is shown in Fig 6-1.

Fig 6-1  Steps in the construction technique of a removable quadhelix.

Fig 6-2  Steps in the construction of a soldered quadhelix. Only the posterior part of the appliance with the loops and the soldered joint is shown. The anterior loops are the same as those on the removable quadhelix.

For the soldered quadhelix, a clinical try-in stage is required. The orthodontist takes an alginate impression with the uncemented first molar bands in place in the mouth. The operator removes the bands and sets them carefully into the impression, which is then poured after a little sticky wax has been dropped inside the bands to secure them (Fig 6-2a). The technician constructs and adjusts the quadhelix and solders it to the bands on the working cast (Figs 6-2b to 6-2d).

Activation

There are two ways to activate the quadhelix before placing it in the mouth. Ricketts et al (1979) originally suggested that operators activate the appliance with a three-pronged pliers to incorporate expansion and molar-rotating force (Fig 6-3). The authors use another method proposed by Kholoki (1995). It employs an arch form chosen from a pentamorphic chart that serves as a pattern for regulating the quadhelix (Figs 6-4 to 6-7).

Fig 6-3  First method for activating a quadhelix. (1) Incorporate a bend in the anterior segment of the wire to lend to it a bilateral expansion force of half a tooth in the molar area. (2) The bend imparts a distorotation to the lateral segments of the device. (Adapted from Ricketts et al 1979.)

Fig 6-4a  Second method for activating a quadhelix. Place the pattern of the chosen arch form on the mandibular cast and make a mark at the site of the mesial surfaces of the first molars. Place the mesial surface of the bands of the quadhelix 3 mm behind this line with the molar tubes parallel to the palatal midline.

Fig 6-4b  To activate a removable quadhelix, place the molar segments parallel to the palatal midl ine 8 to 10 mm inside the pattern, a distance that corresponds to the average buccopalatal diameter of a maxillary first molar. With this maneuver, the device will have the capability to correct molar rotation and accomplish expansion in conformity with the requirements of the specific arch form.

Fig 6-5  Schematic representation of the effects of parallelism on the buccal segments horizontally: (1) When the molars are rotated mesially, the quadhelix is activated in conformity to arch form. The molar segments of the device are parallel to the palatal midline (toe-in information). (2)When one of the two molar segments of the quadhelix is inserted in the palatal molar tube, the contralateral segment will lie distal to its molar. (3) With the two molar segments now set in the tubes, the appliance exerts rotational force on the molars. (4) The mesial rotation of the molars has been corrected.

Fig 6-6a  Quadhelix activated and placed on the cast. The buccal segments of the arch are recontoured thanks to the precise adjustments made in the arms of the helix. They allow the device to conform seamlessly to the prescribed arch form. Make a pliers bend in the canine area to compensate for the difference in thickness between the lateral sectors. Successive activations can be made, if needed, every second or third visit by decementing the soldered quadhelix or by taking out the removable quadhelix and reshaping it. Always use the arch form pattern selected at the start as a guide.

Fig 6-6b  Quadhelix in place on the cast.

Fig 6-7a  Schematic representation of how the quadhelix works in the transverse plane. (1)Initial position of the molars. CRS, center of resistance. (2)The expansion information incorporated in the quadhelix will move molar crowns buccally (force applied at a distance from the center of resistance). (3)To accomplish bodily movement of the molars, buccal root torque must also be applied; to avoid the unwanted side effects of extrusion or intrusion, torque must be equivalent on the two sides. (Adapted from Kholoki 1995.)

Fig 6-7b  Method for assessing the preactivated torque. Place a cotton roll in each molar band and see if the protruding parts are parallel, which would indicate that the torque force is zero. If they diverge, pointing up and outward, the torque is acting buccally. This information must be incorporated in the appliance if it is to act orthopedically. Torque force is imparted to the soldered part of the band for the cemented quadhelix and to the molar segment that is inserted in the palatal tubes for the removable quadhelix; the wire, being bent on itself, functions like a rectangular arch.

Fig 6-8  Crozat quadhelix. Transform a quadhelix into a Crozat quad-helix by soldering two anterior Elgiloy 0.024 springs that will rest on the cingula of the maxillary incisors and on the lateral arms. Extend the springs to the distal surface of the opposing canine. A compensatory loop in the canine area makes it possible to activate the springs as they move the incisor teeth labially.

Fig 6-9  Quadhelix with spurs. Solder spurs, in the form of 0.036 wire loops, to the palatal arms of the quadhelix.

Fig 6-10  Crozat bihelix.

Crozat quadhelix

Construction of a Crozat quadhelix is shown in Fig 6-8.

Quadhelix with lingual spurs

Lingual spurs can be soldered to the quadhelix (Fig 6-9).

Bihelix

Laboratory steps

The alginate impression is poured with the tried-in molar bands set in place. This should be a good, deep impression that accurately reproduces the lingual area and the lingual frenum. The appliance is constructed in blue Elgiloy 0.036 wire in the same way as a soldered quad-helix without anterior loops.

Crozat bihelix

The Crozat bihelix (Fig 6-10) is distinguished from a simple bihelix by the anterior springs soldered to the lateral arms that are used to move the mandibular incisors labially.

Indications

1. Distolingual rotation of maxillary molars so that they can occlude correctly with their mandibular counterparts

2. Recontouring of the mandibular alveolar shelf to provide increased arch length

3. Expansion of the anterior region to create space for labial movement of the incisors

4. Molar anchorage

5. Space maintenance

Activation

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